1. Field of the Invention
The present invention relates to a communication apparatus, a communication method and programs, more specifically to a communication apparatus for performing communication using a transmission scheme that is selected from a plurality of preset transmission schemes, a communication method thereof and programs therefor.
2. Description of Related Art
A wireless communication apparatus tends to encounter higher data error rate as compared to a wired communication apparatus. In particular, throughput in a wireless communication varies largely depending on radio wave transmission environment such as multi-path, fading and the like. As a countermeasure, the wireless communication apparatuses to be used in, e.g., wireless LAN and the like are typically provided with means for improving communication quality by changing a transmission rate in response to switching of a coding rate in a convolutional encoder or a transmission scheme such as a modulation method and the like in a modulator.
In this case, manual switching of such transmission scheme by a user is very complicated and adversely affects its operability. It is therefore typical to provide means for automatically switching transmission schemes depending on communication conditions. Such technologies are commonly known as fall back, fall forward, rate adaptation, link adaptation, or the like.
FIG. 16 is a graph showing an example of such automatic switching of transmission schemes in accordance with the communication conditions. In FIG. 16, the vertical axis represents a transmission rate corresponding to transmission scheme 1 to transmission scheme 6 while the horizontal axis represents time. It should be noted that the ideal maximum transmission rates of the respective transmission schemes sequentially increase in the order of the transmission scheme 1 to the transmission scheme 6. In the particular example as shown in FIG. 16, the transmission schemes are switched to a lower maximum transmission rate at time t3 and time t6 while to a higher maximum transmission rate at time t4 and time t5.
As a criterion in making decision whether or not the transmission scheme should be automatically switched, it is typical to use a measurement result of one type of transmission path property. For example, if an error rate becomes lower than a predetermined threshold value, it can be assumed that radio wave transmission environment is in good condition. Accordingly, the transmission scheme is switched to that of a higher transmission rate in which the error rate may be slightly higher. On the other hand, if the error rate becomes higher than another threshold value, it can be assumed that the radio wave transmission condition is in poor condition. Accordingly, the transmission scheme is switched to that of a lower transmission rate in order to improve the error rate. In this manner, the transmission scheme is selected so as to obtain the highest transmission rate as possible with reducing the error rate at the same time.